Wu Shiping

Research on Mould Filling and Solidification of Titanium Alloy in Vertical Centrifugal Casting

Abstract The objective of this paper is to study the filling process of titanium alloy melt in vertical centrifugal casting, as well as the effect of processing parameters on the formation of defects of titanium alloy castings. Experimental results show that the castings obtained in the centrifugal field are better than that obtained in the gravity field. The molten metal sticks to one side of the mould which is opposite to the rotational direction to fill in the vertical centrifugal field. And the cross-sectional area of the molten metal in the runner decreases with increasing of filling length, but has a back-up trend at the inlet of ingate due to the decreases of filling velocity at the ingate. The processing parameters such as rotational direction, rotational radius and rotational velocity play an important role in the formation of defects of titanium alloy castings. Different rotational direction leads to different filling sequence of molten metal, which then affect the following solidification and the formation of the defects. Under the given rotational velocity, the volume of inner defects of castings decreases with increasing of rotational radius and rotational velocity.

Optimization of low-pressure die casting process parameters for reduction of shrinkage porosity in ZL205A alloy casting using Taguchi method

In order to reduce serious tendency of the shrinkage porosity in ZL205A alloy, the design of experiment technique, Taguchi method is introduced to optimize the process parameters of cylindrical shell ZL205A alloy parts produced by low-pressure die casting in this article. The effect of pouring temperature, filling time and packing pressure on the shrinkage porosity in ZL205A castings is investigated using the orthogonal array and Advanced Porosity Model in ProCAST to calculate the volume of shrinkage porosity. The effectiveness of selected casting parameters in reducing the shrinkage porosity in cylindrical shell ZL205A casting is verified through analysis of signal-to-noise ratio and analysis of variance. Numerical results indicate that the optimized process parameters, including a pouring temperature of 725 °C, filling time of 20 s and packing pressure of 175 kPa, can be used to reduce the formation of shrinkage porosity in ZL205A castings.

Numerical simulation of off-centred porosity formation of TiAl-based alloy exhaust valve during vertical centrifugal casting

The vertical centrifugal casting method has been used to cast a TiAl-based alloy exhaust valve. Although mould filling and solidification of TiAl-based alloy melt proceed under pressure generated by the centrifugal force, an unfavourable solidification sequence is formed because of the special mould filling mode and finally results in the formation of off-centred porosity. Numerical simulation is applied to study the vertical centrifugal casting process of the TiAl-based alloy exhaust valve in this paper. On the basis of simulations of the flow field and the temperature field, the law of porosity formation during the vertical centrifugal casting of the TiAl-based alloy exhaust valve is discussed by analysing the mould filling and solidification process. The results of the numerical simulation show that off-centred porosity forms easily near the entrance of the cast product and the tendency for off-centred porosity formation decreases with increasing distance from the entrance to the far end. The experimental results agree well with those of the numerical simulation.